A Report That Cannot Be Used Is Not Evidence
Most suppliers will send a test report when asked. Far fewer send one that lets a buyer verify that the part matches the drawing. Reports that list “tested: OK” against five lines are not quality evidence; they are a courtesy. This is the minimum content that makes a report auditable, and the questions that expose the gaps.
The Minimum Content
| Section | What must be there | Why buyers need it |
|---|---|---|
| Identification | Part number, drawing revision, lot or date code, quantity tested | Without the revision, the report certifies a part that may no longer be the one you buy |
| Instrumentation | Instrument model, calibration date, last cal due | An uncalibrated LCR meter produces numbers that cannot be defended in an audit |
| Test conditions | Frequency, test voltage, DC bias current, temperature, and the fixture used | Inductance measured at 1 kHz is not the inductance your converter sees at 100 kHz with bias |
| Electrical results | Inductance with min/typ/max, leakage inductance, DCR, turns ratio, polarity, hipot, insulation resistance | The pass/fail limits must come from the drawing, not from the supplier’s own practice |
| Temperature data | Winding resistance before and after the run, ambient, rise in kelvin, duration | Rise is the number that predicts field life; a spot temperature reading is not the same measurement |
| Materials | Core grade, wire type and class, insulation system reference, varnish | Substitution is the most common silent change, and it is invisible in the electrical results |
| Sample size and judgement | Number tested, number passed, the sampling plan, and who signed | “All passed” from an unstated sample is not a statistical statement |
| Photos | Winding, termination, marking, and the label on the carton | Catches construction errors that electrical tests pass, such as a missing margin tape |
The Five Questions That Find Weak Reports
- At what bias current was the inductance measured? A gapped inductor specified for 10 A that was measured at 0 A tells you nothing about its behaviour in the circuit.
- Was hipot applied at the drawing’s voltage, for the drawing’s duration? Reports often show 1 kV for 1 s when the requirement was 3 kV for 60 s.
- Is the temperature rise from resistance change, or from a thermocouple on the surface? Only the resistance method captures the winding interior.
- Which revision of the drawing was the part built to? If the report does not name a revision, it cannot be compared with the drawing you are approving.
- Who signed, and in what capacity? A signature with no name and no role is not traceability.
What to Require by Shipment Type
- First article: the full report above, plus dimensional report and material declarations.
- Production lots: a certificate of conformity referencing the first-article report, plus electrical results for the sample drawn, plus hipot on 100 % of units for safety-critical parts.
- After any change: a new first article. A changed core grade, wire supplier, varnish or winding machine is a new part in everything but the part number.
Related reading
- Hipot and Partial Discharge Testing
- Insulation Resistance vs Hipot
- First Article Inspection Reports
- Inductance Tolerance and Converter Performance
Every SiRui shipment carries a report built to this structure, with the test conditions and the drawing revision stated. Ask the Magnetic Core team for a sample report before you place the order: sales@sirui-tech.com.